338 BACTERIOLOGY. 



the water interferes with the development of the colonies 

 as isolated points and causes them to become confluent. 

 To obviate this he recommends that the agar-agar be 

 poured into the plates and the water allowed to separate 

 from the surface at the temperature of the incubator 

 before they are used. It is wise, therefore, when one 

 is liable to be called on for such work as this to keep a 

 number of sterilized plates of agar- agar in the incubator 

 ready for use, just as sterilized tubes of media are 

 always ready and at hand. The advantage of using 

 the agar plates is the higher temperature at which they 

 can be kept, and consequently a more favorable condi- 

 tion for the development of the colonies. As soon as 

 isolated colonies appear they should be examined mi- 

 croscopically for the presence of organisms having the 

 morphology of the one for which we are seeking, and 

 as soon as such is detected gelatin plates and cultures 

 in peptone solution (for the indol reaction) should be 

 made. The peptone cultures started from the original 

 material should be examined microscopically from hour 

 to hour after the sixth hour that they have been in the 

 incubator. The material taken for examination should 

 always come from near the surface of the fluid, and 

 care should be taken not to shake the tube. As soon 

 as comma bacilli are detected in anything like consid- 

 erable numbers in the upper layers of the fluid agar- 

 agar plates and fresh peptone cultures should be made 

 from them. The colonies will develop on the agar-agar 

 plates at 37° C. in from ten to twelve hours to a size 

 sufficient for recognition by microscopic examination, 

 and from this examination an opinion can usually be 

 given. This opinion should always be controlled by 

 cultures in the peptone solution made from each of 



